Most motor vehicles that operate on roads and highways typically have an occupant compartment, where the driver and any passenger or passengers sit, and in front of the occupant compartment, an engine compartment for housing the engine that propels the vehicle.
Certain electrical devices, such as driver information displays and various controls, are present inside the occupant compartment. Certain ones of those devices need to be in electrical communication with vehicle components that are disposed outside the occupant compartment. Those components include the engine and the transmission through which the engine is coupled with the drivetrain.
Consequently it is common practice to bundle wires into wiring harnesses having some connectors that make connections to electrical devices inside the occupant compartment and other connectors that make connections to components that are outside the occupant compartment. Necessarily such harnesses must pass through a wall shared by the two compartments. Such a wall is sometimes referred to as a dash panel, or simply a dash.
Because a number of vehicle components and systems are disposed on or in close proximity to the dash, available space for routing wiring harnesses through the dash is typically at a premium. The location of a wiring harness pass-through in the dash is not the only consideration in the design phase of motor vehicles; the nature of the pass-though is also a consideration.
One type of pass-through comprises a grommet that fits to a through-opening in the dash and through which bundled wires pass. Such a grommet may be affixed in some suitable way to the bundled wires so as to be immovable along the length of the harness. Installation of such a harness involves feeding one or more connectors through the through-opening and then pulling the harness until the grommet seats in the through-opening. In that type of pass-through, any connector that must be fed through the dash opening must be small enough in size to freely pass through.
Another type of pass-through is somewhat different in that the through-opening in the dash serves as the location where a harness that is inside the occupant compartment mates with a harness that extends into the engine compartment. Mating of the two harnesses is via one connector in one harness mating with another connector in the other harness at the dash. These are sometimes referred to as bulkhead connectors. For example, the occupant compartment harness can terminate in a connector that fits to the through-opening on one side of the dash and is mounted in any suitable way to the dash. The other harness terminates in a mating connector that plugs into the connector on the occupant compartment side of the dash. This type of pass-through is typically more expensive not only because the bulkhead connectors are required, but because other design and manufacturing issues often arise.
One of those other issues may be the sequence of steps in assembling a vehicle. Certain motor vehicles have what is sometimes called a body-frame construction. A frame provides the structure for mounting chassis components that form the vehicle powertrain. A body forms the occupant compartment, and at some point in the vehicle assembly process, the body is placed on and fastened to the frame. In the case of a truck, the body is sometimes referred to as the cab.
Assuming that many powertrain components, including the engine, transmission, and drivetrain, have been already mounted on the frame at the time that the body is placed on the frame, it then becomes necessary to make connection of engine compartment wiring harness connectors with corresponding occupant compartment wiring harness connectors. Available space considerations after body placement may render it difficult for assembly line personnel to efficiently make those connections.
Certain vehicle models that use essentially the same platform may have different electrical devices and components from vehicle to vehicle. Consequently, while the vehicles are generally similar, the wiring may differ from vehicle to vehicle. This means that some wiring harnesses may have more wires in a bundle and other harnesses fewer wires. Consequently, the diameter of a wiring harness passing through the dash in some vehicles will be larger than in others. The wiring harness through-openings in a dash panel are typically created at the time the dash panel is manufactured, typically by punching in sheet metal during the dash panel stamping process. While it would be possible to manufacture dash panels with different sized wiring harness through-openings, that would introduce complexities that would far outweigh the benefits. Therefore it is typical for a wiring harness through-opening in a dash that is common to different vehicle models to have a common size that can accommodate wire bundles of different diameters depending on the particular number and size of wires in a harness needed to satisfy requirements for the respective models and their electrical equipment.
Sealing of a grommet to bundled wires in a wiring harness may also be important in order to provide weather—and sound—tightness through the grommet. U.S. Pat. Nos. 5,270,487 and 6,402,155 are examples of grommets that have sealant within the grommet that aids in sealing to the wire bundle passing through the grommet opening.